1. Field of the Invention
The present invention relates to a differential pressure operating valve which controls a vacuum suction force of an object to be sucked, an exposure apparatus which transfers a fine pattern onto a substrate such as a wafer, and a device manufacturing method.
2. Description of the Related Art
Recently, in an exposure apparatus used for manufacturing a device such as a semiconductor or a liquid crystal, a high accuracy and a high functionality are required in accordance with an improvement of the productivity for responding to the rapid increase of demand and a high integration. Therefore, the development of an exposure apparatus having a high throughput and a high transfer performance is desired.
In such an exposure apparatus, a substrate holding apparatus which holds a substrate such as a wafer includes a wafer chuck or the like which sucks the wafer by a predetermined vacuum suction force.
The wafer chuck receives a wafer from a conveying hand at a wafer supply position far from a focus position of a projection optical system included in the exposure apparatus. The wafer chuck also sucks to hold the received wafer by the vacuum suction force to move it to the focus position. After the exposure is finished, the wafer chuck moves from the focus position to a wafer recovery position. The conveying hand recovers the wafer from the wafer chuck at the wafer recovery position. The exposure apparatus repeatedly performs each of the processes.
Conventionally, there has been one line which generates a vacuum suction force to the wafer chuck of the wafer stage, and the vacuum suction force has been generated by performing an ON/OFF switching. The vacuum suction has started before the transfer so as not to cause a position displacement at the time of transferring the wafer.
Therefore, the exposure apparatus is in an air blank suction state in an interval after the vacuum suction starts before the wafer is mounted on the wafer chuck. Therefore, a problem that much time is necessary after the wafer is mounted on the wafer chuck and before a required suction pressure is achieved is generated. The similar problem is also generated in a reticle chuck on a reticle stage, a reticle conveying robot, a wafer conveying robot, or the like. Further, when a vacuum suction force immediately before the wafer is mounted on the wafer chuck is large, a problem that the wafer is distorted to be sucked is also generated.
With regard to the problem, Japanese Patent Laid-open No. 2002-343852 discloses a suction force variable mechanism which selects two suction lines using an electromagnetic valve that is a switching unit to change the vacuum suction force in two stages for optimizing the vacuum suction force of a wafer chuck.
However, in the suction force variable mechanism disclosed in Japanese Patent Laid-open No. 2002-343852, an electric system or a control method is complicated, and its configuration has to be large in size. Therefore, such a suction force variable mechanism is disposed at a pipe unit far from the wafer chuck, and it requires much time to increase the vacuum suction pressure of the chuck portion after the vacuum suction is turned on, which causes a reduction of throughput.
Japanese Patent Laid-open No. 06-262464 discloses a vacuum suction apparatus which sucks to fix a work by a pressure difference.